An example for the stristr() function:
<?php
$a = "I like php";
if (stristr("$a", "LikE PhP")) {
print ("According to \$a, you like PHP.");
}
?>
It will look in $a for "like php" (NOT case sensetive. though, strstr() is case-sensetive).
For the ones of you who uses linux.. It is similiar to the "grep" command.
Actually.. "grep -i".